The present invention relates to an optical information storage device for accessing information by irradiating a light on a surface of a recording medium, and an optical head used for such an information storage device.
Conventionally, as a medium for storing a voice, image information, a character, a computer program or the like, an optical disk such as a CD, a CD-ROM, a CD-R, a DVD, a PD or an MO, has been known. An optical information storage device has also been known, which forms a condensing spot by using the optical head to condense a laser beam or the like on such an optical disk, and accesses the optical disk by using the condensing spot. Such an optical information storage device is now a focus of attention because of portability of a recording medium, a large capacity and a light weight. With achievement of higher performance of a computer in recent years, there is a demand for a great increase in an information recording density by such an optical information storage device.
The information recording density by the above-described optical information storage device is higher as a size of the condensing spot on the optical disk is smaller. Thus, developments of a shorter wavelength laser beam source, and studies of a higher NA of an objective lens have been actively conducted. Regarding achievement of the higher NA of the objective lens, there has been known a method for realizing an objective lens, which has a numerical aperture set to exceed 1 and reach about 1.4 by condensing a light in a medium of a high refractive index, as in the case of an oil immersion lens of an optical microscope. However, the size of the condensing spot cannot be greatly reduced by the shorter wavelength of the laser beam source or the higher NA of the objective lens, and thus it is difficult to greatly increase the recording density. In addition, a technology has been presented, which physically forms a condensing spot of a smaller size by using a pinhole. However, in the technology using the pinhole, a quantity of light is small, efficiency of light utilization is 0.1% or lower, and positioning of the condensing spot with respect to the pinhole is difficult. Thus, there are difficulties of stable information accessing, high-speed information transferring and reproducing. Moreover, during tracking, the condensing spot and the pinhole must be translated at a high speed. However, it is difficult to realize a low-priced actuator or the like for moving the pinhole at a high speed.
With respect to the foregoing technologies, a magneto-optical recording technology based on a laser pulse magnetic field modulation system has been presented, which records information by a mark length smaller than the size of the condensing spot. To greatly increase the recording density, narrowing of a track pitch is essential. In the above-described magneto-optical recording technology, however, it is impossible to narrow such a track pitch.
The present invention has been developed to solve the foregoing problems, and an object of the present invention is to provide an optical information storage device capable of performing stable information accessing at a high recording density, and an optical head.
In order to achieve the foregoing object, in accordance with a fist aspect of the present invention, there is provided an optical information storage device for performing information access by irradiating a light on a surface of a recording medium, the recording medium having a track irradiated with the light to at least reproduce information, comprising:
a medium holding section for holding the recording medium in a predetermined position; and
an optical head for irradiating the light on the surface of the recording medium held by the medium holding section,
wherein the optical head includes
a light source for emitting a light,
a light shielding body provided with a slit,
a light shielding body holding section for holding the light shielding body in a position close to/in contact with the surface of the recording medium such that the slit of the light shielding body intersects the track by an angle of 45xc2x0 or lower,
condensing means for condensing the light emitted from the light source on the slit of the light shielding body, and
moving means for moving the light condensed on the slit by the condensing means along the slit.
According to the optical information storage device of the first aspect in the present invention, preferably, the holding section holds the light shielding body such that the slit of the light shielding body intersects the track by an angle of 5xc2x0 or lower.
In order to achieve the foregoing object, in accordance with a second aspect of the present invention, there is provided an optical information storage device for performing information access by irradiating a light on a surface of a recording medium, the recording medium having a plurality of linear tracks provided at predetermined intervals on the surface and irradiated with the light to access information, comprising:
a medium holding section for holding the recording medium in a predetermined position; and
an optical head for irradiating the light on the surface of the recording medium held by the medium holding section,
wherein the optical head includes
a light source for emitting a light,
a light shielding body provided with a slit,
a light shielding body holding section for holding the light shielding body in a position close to/in contact with the surface of the recording medium such that the slit of the light shielding body intersects the tracks by an angle of 45xc2x0 or lower,
condensing means for condensing the light emitted from the light source on the slit of the light shielding body, and
moving means for moving the light condensed on the slit by the condensing means along the slit by changing an incident angle of the light made incident on the condensing means, and
a following relationship is established among an interval Tp between the tracks, a focal distance f of the condensing means, a minimum changing amount xcex94xcex8 of angle changed by the moving means, and an angle xcex1 of intersection of the slit with respect to the tracks:
Tp/(sin xcex1xc2x7fxc2x7xcex94xcex8)xe2x89xa710 
In this case, any tracks can be used as long as they allow information to be linearly recorded. The tracks are not limited to those physically formed as grooves, and tracks formed only magnetically or optically on a plane may also be used.
The xe2x80x9cslitxe2x80x9d means an optical slit. Any slits can be used as long as they diaphragm luminous fluxes only in a predetermined direction, and a slit having a light transmitting portion filled with a transparent material such as glass may also be used.
In addition, the light shielding body holding section may be a carriage moving on a rail, or a swing arm rotating around a predetermined point of view. The carriage or the swing arm may hold a slider having the light shielding body loaded.
According to the optical information storage device of each of the first and second aspects of the present invention, since the slit intersecting the track by the foregoing angle physically reduces a size of the condensing spot in a slit width direction, a track pitch can be narrowed. As a result, it is possible to perform information accessing at a high recording density. Especially, by using the device in combination with a magneto-optical recording technology based on a laser pulse magnetic field modulation system, a very high recording density can be realized. Because of no eclipsing of the condensing spot and no losses of efficiency of light utilization in a longitudinal direction of the slit, the efficiency of light utilization is high, and the recording medium can be irradiated with a sufficient quantity of light. As a result, it is possible to perform stable information accessing and high-speed data transferring. Moreover, since the light condensed on the slit is moved along the slit by the moving means, tracking accuracy is high in a direction orthogonal to the track, and thus it is possible to perform meticulous tracking control.
According to the optical information storage device of each of the first and second aspects of the present invention, preferably, the condensing means of the optical head condenses the light to be in a long elliptic shape in a direction parallel to the track of the recording medium. Because of such an elliptic shape of the condensing spot, accuracy of positioning the condensing spot with respect to the slit in the direction parallel to the track may be lowered.
In addition, if the condensing means of the optical head condenses the light to be in such an elliptic shape, preferably, the condensing means includes a cylindrical lens provided on the slit of the light shielding body so as to direct a bus in a direction orthogonal to the track of the recording medium, and the light is condensed through the cylindrical lens. Furthermore, preferably,
the light source emits infrared rays,
the light shielding body is made of silicon, and
the condensing means includes a cylindrical lens made of a semiconductor transmitting the infrared rays.
The condensing means forming the condensing spot in the elliptic shape can be realized in a simple structure by using the cylindrical lens. In addition, the light shielding body and the cylindrical lens made of the foregoing materials can be mass-produced inexpensively by using a photoetching technology or the like.
In order to achieve the foregoing object, in accordance with the present invention, there is provided an optical head comprising: a light source for emitting a light;
a light shielding body provided with a slit for guiding a light to a surface of a recording medium;
condensing means for condensing the light emitted from the light source on the slit of the light shielding body; and
moving means for moving the light condensed on the slit by the condensing means along the slit.
The optical head of the present invention is used for an optical storage device, and the slit provided in the light shielding body of the optical head intersects the track of the recording medium by the foregoing angle, and thus, it is possible to perform stable information accessing a high recording density.
In addition, according to the optical head of the present invention, preferably, the slit provided in the light shielding body has a width set equal to or less than xc2xd of a wavelength of the light emitted from the light source. Because of the slit provided to have such a width, a light called near light is oozed out from the slit to form a fine spot, making it possible to access information at a much higher recording density.
Furthermore, according to the optical head of the present invention, a coil may be provided along the slit of the light shielding body held in the position close to/in contact with the surface of the recording surface.
To generate a magnetic field necessary for magneto-optical recording by a laser pulse magnetic field modulation system on the surface of the recording medium, the coil must be brought close to about 10 xcexcm from the surface of the recording medium. The foregoing coil can be brought sufficiently close to the surface of the recording medium.
As described above, according to the optical information storage device and the optical head of the present invention, it is possible to perform stable information accessing at a high recording density.